The invention relates to an apparatus that allows an isochronic transmission route (i.e., a digital transmission route operated with a given system clock pulse) to transmit anisochronic data (i.e., data with a frequency different than the operating frequency of the transmission route).
The transmission of data (e.g., audio data) having a particular assigned frequency for further processing or reproduction can encounter the problem that the data must be transmitted on a clocked transmission route whose operating frequency differs from this assigned frequency. One possibility of transmitting anisochronic data on such a route is to convert the assigned frequency to obtain an intermediate data stream with the operating frequency of the transmission route. The intermediate data stream is transmitted over the transmission route, and at the receive side converted again to the assigned frequency. For example, in the case of a data stream that includes an audio signal whose assigned frequency is the sampling frequency of the audio signal, this frequency can be converted by converting the signal to an analog signal and then sampling and redigitizing the analog signal at the operating frequency of the transmission route.
However, a problem with this technique is that it is relatively complicated and expensive because of the rate converters needed at both ends of the transmission route. In addition, performing a digital-to-analog conversion and an analog-to-digital conversion causes a loss of quality in the audio signal and generally a loss of some information. If the operating frequency of the transmission route is less than the original sampling frequency, information loss is unavoidable even if the analogizing and digitizing processes are assumed to be ideally error-free, because high-frequency spectral components are suppressed during transmission.
Therefore, there is a need for an apparatus that provides a transmission system to transmit an anisochronic data stream, regardless of the operating frequency of the transmission route and of the frequency assigned to the data stream.